In some industrial settings, it is necessary to provide a sealed environment around electronic equipment in order, for example, to prevent an explosion that could be triggered by the electronics. In such an environment, outputs may be viewed and controls accessed through a sight glass, which is typically a thick glass disk, e.g., 8 mm, held between two metal frames. The metal frames are generally secured by bolts and gaskets, although alternatively, the glass disc can be fused to the metal frame during manufacture. To access the controls, the sight glass is openable, generally with protocols indicating the conditions under which the sight glass can be opened to access underlying controls. A means of providing input to the electronics underlying the sight glass without opening the sight glass is desirable. Capacitive touch detectors are successfully used in many consumer products, e.g., indium tin oxide (ITO)-based solutions for touch screens on computers and cell phones, but will not work in these industrial settings, given the thickness of the glass.